This project attempts to further understanding of the mechanism of estrogen action by elucidating the molecular basis of hormone-induced transformation of the receptor protein of uterine cytosol from the native (4S) to the active (5S) form, similar to that extracted from uterine nuclei. Purified preparations of both the cytosol and nuclear estradiol-receptor complexes are being isolated in amounts permitting immunochemical proof of purity, end group analysis and determination of aminoacid composition and sequence.